In order to conform to the National Television Standards Committee (hereinafter NTSC)/Phase Alternating Line (hereinafter PAL) standards for color television, a NTSC/PAL encoder interleaves the luminance and chrominance components in an intricate manner to conserve bandwidth and ensure compatibility with monochrome televisions. However, as the NTSC/PAL encoder processes higher resolution inputs because of the usage of higher resolution cameras, computer-based graphics animations, etc., proper decoding of such inputs is becoming increasingly difficult for a traditional NTSC/PAL decoder.
FIG. 1 illustrates prior art digital decoder 100 for a NTSC/PAL television receiver. Digital decoder 100 operates on composite video signals that conform to NTSC/PAL standards in three main stages. Specifically, after analog-to-digital (hereinafter A/D) converter 102 generates digitized composite signal 104 based on the incoming signals, Y/C separator 106 separates out luminance (Y) and chrominance (C) from this digitized composite signal 104. Because display subsystem 110 typically utilizes cathode-ray tube (hereinafter CRT) technology that uses red, green and blue phosphors to create the desired color, signal adjuster 108 operates further on the newly obtained Y and C signals to generate R (red), G (green) and B (blue) signals. Some of the functions that signal adjuster 108 performs are, but not limited to, chrominance demodulation, brightness, contrast, saturation and hue adjustment, display enhancement processing, color space conversion, pixel formatting, etc.
FIGS. 2(a) and 2(b) illustrate prior art Y/C separator 200 and prior art Y/C separator 220, respectively, for most of the existing NTSC televisions. In particular, Y/C separator 200 is an ordinary two-line comb filter that operates on digitized composite signal 104 as shown in FIG. 1. Y/C separator 200 employs first line delay element 202, second line delay element 204 and adder 206 to generate a double-amplitude output composite video signal 208 (since the sub-carriers for digitized composite video 104 are in phase). Because of a 180° phase difference between output composite video signal 208 and delayed composite video signal 212, subtracting the two signals cancels most of the luminance and leaves double-amplitude chrominance. Bandpass filter 216 further eliminates signals outside of a predefined frequency range for chrominance information to yield signal C. Adder/subtractor 218 then subtracts signal C from delayed composite video signal 212 to generate signal Y.
Y/C separator 200 however has trouble with diagonal lines and vertical color changes. With diagonal lines, Y/C separator 200's C signal as shown in FIG. 2(a) includes the difference between adjacent luminance values, which may be interpreted as chrominance information. Such interpretation results in cross-color artifacts. As for vertical color transitions, the so-called “dot crawl” artifact surfaces due to imperfect removal of color information from Y/C separator 200's Y signal as shown in FIG. 2(a).
Y/C separator 220 as illustrated in FIG. 2(b) is an improved solution over Y/C separator 200. Particularly, Y/C separator 220 includes vertical correlation detector 222, which determines the amount of line-to-line correlation. If line 1 (hereinafter L1) and line 2 (hereinafter L2) are highly correlated, vertical correlation detector 222 causes multiplexer (hereinafter Mux) 224 to select L2-L1 as its output. If L2 and line 3 (hereinafter L3) are highly correlated, the output of Mux 224 is then L2-L3. Although Y/C separator 220 may address the aforementioned cross-color and dot crawl artifacts, it may have problems with real-world video. More specifically, it may not have sufficiently correlated lines to adequately separate the luminance and chrominance signals as occurs with high resolution cameras and computer graphics animation. So, the more detail that is present in digitized composite video 104, the greater the artifacts would be introduced by Y/C separator 220.
As for many of the existing PAL televisions, they utilize Y/C separators that are similar to their NTSC counterparts as shown in FIGS. 2(a) and 2(b). One difference is that a PAL Y/C separator also has a PAL modifier that provides a 90° phase shift and removal of the PAL switch inversion. However, the PAL Y/C separator suffers from Hanover bars that result from a real and complementary hue error between pairs of adjacent lines and also cross-color as mentioned above.
As has been demonstrated, the decoding technologies that exist in many of the current NTSC/PAL televisions are unable to keep pace with the ever increasingly dynamic, complex and detailed video sources. Thus, an apparatus and method is needed to provide a cost-effective, flexible and highly scaleable video decoding solution that not only could accommodate the discussed shortcomings of the current NTSC/PAL television decoders, but also could further improve display quality of NTSC/PAL composite signal on other types of display equipment.